I emphasize the need to preach a single text in most sermons. There are exceptions, but generally one text is the way to go. I want to be clear why I make this suggestion (today) and address a possible misunderstanding (tomorrow).
I strongly suggest preaching on one text most of the time, because it is so easy to scratch the surface of a passage and yet fail to preach the text. Multiplying texts only multiplies the likelihood of missing the point and failing to really preach the text at all. It takes a lot of work to wrestle with a text and have a text wrestle with you. It takes a lot of prayerful thought to engage with historical and written context, to recognize rhetorical structure, to analyze each detail of content, to ascertain authorial intent (purpose as well as meaning) and to synthesize the core idea of a passage. I don’t think I’m being lazy when I suggest taking multiple passages multiplies the workload beyond what most of us can bear (if we are to really preach rather than scratch the surface, or scratch some itchy ears).